Tuesday, February 19, 2008

What a tangled web we unravel

When you stop to realize just how beautifully complex and interdependent Nature's ecosystems are, one has to wonder if we'll ever be able to completely understand them. it seems like the more we learn the less it is apparent that we know.

True we humans are capable of creating our own brand of complex and sophisticated systems. We use them use them to manage and/or outsmart Nature. We've certainly gotten very clever at tracking and netting increasingly larger catches of fish over the years.

CHATHAM — In recent years, Chatham fisherman Peter Taylor noticed that the haddock he'd been catching on Georges Banks disappeared after large herring vessels, some towing nets as wide across as a football field, started targeting that area.

He said prey species like haddock move into certain areas of Georges Bank when there are large schools of spawning herring. Cape fishermen, in turn, go there to catch the haddock.

"I've never gone through a year and seen this few herring," he said. "The amount of haddock we caught in that deep water also dropped. There was no doubt in our minds that there was a correlation between herring and what we catch."

It was a lesson that made a big impression on fishermen: no food, no fish.

"People have been fishing here for hundreds of years and they know that a healthy herring population is key to having other healthy fisheries," said Peter Baker, director of The Herring Alliance, a collaboration of environmental groups dedicated to reforming what they call "industrial" fishing by large herring vessels. The group is concerned the fishing power of these large vessels could bring on a collapse of herring stocks as the foreign factory fleet did back in the 1970s.

Raising the alarm

In December, the Marine Fish Conservation Network, comprising 200 environmental groups, fishing associations, aquariums and marine science organizations, raised the alarm on herring, mackerel, menhaden, squid and other species known collectively as forage fish. They want the National Marine Fisheries Service to give greater protection to forage species that serve as prey for many other fish.

They were especially concerned about the rapidly expanding aquaculture industry's dependence on these fish, an increasing number of which are ground up to produce pellets and fish oil to feed fish raised in aquaculture cages.

"We've created a demand and a need for this ... fishery that I don't think is sustainable," Kenneth Stump, a policy analyst for the Washington, D.C.-based Marine Fish Conservation Network, said of fish food for aquaculture.

A letter signed by 92 U.S. scientists, also released in December, urged the National Marine Fisheries Service to drastically reduce the catch of these forage species because of their importance to the ecosystem.

Forage species eat plankton and provide a vital link from that food source to the protein required by larger predator species.

Stump said he believes herring's role as prey is too important to allow large U.S. vessels to catch them. He advocates a return to a small-boat, inshore fishery. He said guaranteeing the availability of their food will also help commercially valuable fish like cod to recover from decades of overfishing.

But NMFS scientists counter that well-managed fish stocks would be sustainable no matter what their ultimate use.

"If we're harvesting conservatively, we should be able to avoid the large swings in prey population that could cascade through the ecosystem," said Steven Murawski, NMFS director of scientific programs, and a chief scientific adviser.

No easy answers

Predator-prey relationships are complex, and some changes might not yield expected results, Murawski said. For instance, when the foreign fleet decimated New England's herring stocks in the 1960s and '70s, other prey species like sand lances prospered and predators like cod simply switched to them. Murawski pointed out that forage species like herring also eat the eggs and larvae of cod and other larger fish, and that an unfished or lightly fished stock could actually have a negative impact on rebuilding those valuable species.

Stump said it was dangerous to rely on fishing to achieve balance in an ecosystem, and that preserving species that form the base of the ocean food chain was critical.

"We're pretty foolish to presume we have to remove this amount to preserve the balance, given the lack of science," he said.

"We have done a fair bit to understand the role of prey species in the food web," countered Michael Fogarty, an NMFS ecosystem scientist.

NMFS and regional fishery management councils have laid the foundation for ecosystem management by gathering data on fish habitat and by extensive work by regional science centers on predator-prey relationships, Murawski said. Ecosystem management pilot programs are also being drafted. Additionally, fishery management scientists already incorporate natural mortality into their estimates of how much of a species can be caught each year without seriously impacting the population, he said.

"We need to be cautious, but that doesn't mean you don't harvest at all," said University of New Hampshire professor Andrew Rosenberg, the former director of NMFS Northeast region and chairman of the U.S. Census of Marine Life. Of more importance is making sure that there is enough prey in areas of the ocean that are critical to commercial fish stocks, Rosenberg said.

Doug Fraser can be reached at dfraser@capecodonline.com.

Forage fish and aquaculture

Worldwide, wild fish stocks were being caught and fed to caged fish in an aquaculture industry that grew threefold between 1992 and 2003.

It takes five pounds of fish to produce one pound of fish meal.

Fish meal supplying aquacultural and agricultural needs accounted for almost 40 percent of the fish landings globally in 2002.